Transmission testing apparatus



ug. l, 1933. l E' ADLER 11,920,456

TRANSMISSION TESTING APPARATUS Filed June 29, 1931 2 Sheets-Sheet l MN I Patented Aug. 1, 1933 Unirse srArEs 1,920,456 `'raANsMIssIoN TESTING APPARATUS Lee E. Acier, Dallas, Tex.

This invention relates to testing sets for meas uring voice transmission eiciency of the telephone lines, broadcasting lines, the efficiency of apparatus associated therewith and other circuits. Q

Generally,'the Vobject of the invention is to provide testing sets comprising two light and compact portable units, an oscillator unit and an indicator unit, each in its separate carrying case or box whereby the sets-will be serviceable in field tests. The oscillator unit has the function to transmit an `alternating current of predetermined amount into the lines or equipment which are subjected. to the test measurements at an average frequency of speech current, 1000 cycles or over a range of frequencies as desired. The indicator unit has the function to measure the proportionate amount of 'the current transmitted from the oscillator unit which is received by the indicator and to indicate the amount of said current directly on a scale calibrated in units of current'or preferably in accordance with this invention to indicate the proportionate amount of said current on a scale calibrated in decibelsv to show directly the eiliciency of the line or equipment in terms of telel phone transmission units so that the usual calculations to determine these measurements will be unnecessary, With these units the sets are ready for immediate use requiring no accessories, complicated preliminary balancing or outside power.

Another object is to provide the testing sets with rugged but sensitive types of rectifying meters requiring small battery power in the oscillating unit oniy and 4which will have greater sensitiveness and require very much less power than thermo-couple type sets and are therefore more economical as well as more serviceable than such sets which require vacuum tube amplification in both transmitting and receiving ends.

A further object is to provide for changing the scale range oi the meter in the indicator coil.

Figures 5 to 9 linclusive are similar diagrams l showing other 'applications `of units inf: measuring telephone receivers fand transmitters,-se ries loss, parallel or bridged loss,.cross talk and loop attenuation `i'n'ea'surt-:ments respectively.

Refer-ring to the drawings, in Figure l .fa vacuum tubetype of oscillating unit arranged in a portable form ina case .designated 10 is shown with its terminal members 11 and 12 connected Pars-Nr the arrangement as shownwin s with wires 13 and 14 of telephone transmission the transmission lines 18 which may contain various transmission line accessories. such as amplifiers, etc. is thus connected with 'the o s cillator unit and indicator unit subject to being tested for transmission losses, or gains, as the case may be.

The oscillator unit, includes ari oscillating.

circuit 19 the output of which feeds throughU a transformer 20 to the oscillator output circuit 2l for supplying an alterna-ting current of audio frequency'to the transmission lines, or apparatus, to be tested. v

Oscillating circuit 19 includes a three electrode vacuum tube 22 which receives its energy from an A battery 23 which is controlled by a key type switch 24 and is adjusted by a rheostat 25. supplied with current from a B battery 26, the negative terminal of which is connected with the negative terminal of A battery 23 and from the positive terminal of B battery 26 the circ-uit The plate circuit of oscillatorrtube 221s includes the primary coil 27 of transformer 20 as the output of the oscillating circuit and from thence it is connected with the plate of tube 22. The grid circuit of oscillator tube 22 includes an inductance 28 which is connected between the grid of this tube and the common negative side of the A and B batteries. A condenser 29 coupling inductance 28 with the plate circuit is connected across `the plate and grid circuits of oscillator tube 22 and may beyaried t produce the desired frequency of the oscillator.

Oscillator output circuit 21 includes the secondary 30 of transformer 20 which feeds thalternating current produced "by the'oscillating circuit through a resistance 31 for adjusting the current output current to the `lines"or`ap paratus under test by changing .the potential. applied thereto. Then a pad oroartincia'l line consisting of a combination of rsistances 32' A.which may lb@ .exchanged s0 es te intresse@ losses of a varied number of transmission ,units .orrdecibels as may be .desired .undef .Ciain :tests iS next .connected in the voutput 1circuit. A condenser 4.32 is provided t0 more@ the meter .and .other apparatus. .fr .ffm @mage by eX- cessive current from outside sources. .outnut circuit is measured .by an .alternating curfrentniilliammeter 33 connected .this .irut between transformer 20 and resistance 3 1, -`reerred to hereinbefore.

The receiving or indicating unit includes min itsrwt .Connected with ,terminals 16 .and 17 acondenser 3.4, ,a pad V3.5 and then .a reQ-er .type .dof meter 36 which is calibrated .with a decibel scale 37 and also a milli-ampere scale 3B, .the latter being provided in order that actual .current values may .be read .by the indicator unit as .well as the oscillator unit lwhen desired.

.The indicating .unit also has a .choke ,coil indnctance 39 bridged across its circuit to effectively .eliminate low frequency line noises Awhichlmight .otherwise interfere .with .the obtaining of accurate measurements, and thus no 'trouble should -be .experienced from .such sources as long as .the line under .Consideration is notv so noisy as to be uncommercial. A key switch 40 is `operable to connect .pad 35 in or out of .the circuit. When the key switch .member is thrown to the left ,contacts .41 are brought into engagement properly connecting the pad in the circuit, .and .when thrown to the right contacts 42 are brought into engagement .connecting conductors 43 and 44 for vshort cir- .cuiting the series connected resistances of the pad in indicator circuit to extend the scale readings ofthe meter 3.6 to a maximum. Pin jacks 45 .are also provided in the receiving or indicator unit to enable the tester or monitor to listen withv a telephone receiver 46 for the cycle' tone from the oscillator unit before attempting to obtain readings on meter 35. Such pin jacks are .also .provided in the oscillator unit and these jacks are connected across the circuits with small condensers 47 in series with them.`

In practice these oscillating and indicating units are self contained portable sets, the casings containing the equipment above set forth, and the oscillating unit having space therein for the and B batteries. .The A battery consists ci two 4.5 volt block type dry cell batteries connected in 'parallel andthe B battery consists of two 22-1/2 tvolt dry cell batteries connected in series. The plate circuit of the oscillator tube employed for tests is 1000 cycles, (however small yariations from 800 to 1200 cycles may be used without perceptible error in the calibration of the indicatori 'and in field calibration of the ',osrcillatorba pitch pipe producing 1000 cycles may b e employed when adjusting the frequency by listening lin'thetelephone receiver 46 connected in lpin jacks 45 provided for that purpose. Milli-ammeter 33 in the output circuit of the oscillating .unit is `a rectifying type designed for a-maximum output of about 5 mia. into a circuit of 500 ohms.

In .the receiving ,or indicating unit fthe milliammeter 36 is designed for reading sion losses directly, without the Kuse of Qamplifier circuits,'tubes and batteries, and-is calibrated in uni-ts ofvoice transmission reading up to w15 decibels directly at a frequenoyfof v11,000cycles with the pad. 35 ffin for measurements ,oi this type, or on-the mil-ampere scale in actual v`current values -for other .types .of measUlQmentS vf Ol whichv the indicator Aunit may be employed. Pad 35 is the equivalent of 10 d.b. with .a terminal impedance of 500 ohms, and by shifting the key 1110 of switch 40 from in position to out position the scale of meter 36 is extended to a maximum of 25 db.'

In order to make attenuation measurements on yoice frequency telephone circuits and apparatus the oscillator unit is rst adjusted to the -desired rfrequency (1000 cycles) as follows: Key switch 24 is closed and rheostat -255 adjusted so that the proper filament current is obtained in the tube y22l (and amplifier tube) and then-by aid of the 120 telephone receiver connected with pin jacks 45, in the oscillator unit, the tone of the oscillations is determined and adjusted to the required frequency according to the frequency of the A pitch pipe or the like. Fine adjustment of the' frequency is provided by varying the capacity oi condenser 29 and also by varying the filament current by rheostat 25. When the oscillator unit has been adjusted the receiving or indicating unit terminals 16 and 130 17 are connected direct to terminals 11 and 12 of the oscillator unit and with the key of switch 40 to pad in position resistance 3l ofthe oscillator unit is adjusted until meter 3 6 of the indicating unit reads o ab. with these adjustments made the reading of meter 33 is noted and the two units are ready for eld tests.

The'instruments are then ready to set up diierentpoints along the transmission line for making measurements of the section of line therebetween. With the units so connected (as shown in Figure 1) the oscillator is adjusted so as to transmitinto the line the alternating cur rent at the predetermined quantity, the exact reading of meter 33 previously noted, and the Afrequency employed for the measurements, 1000 cycles; at then indicator unit by means of a telephone receiver, 46, plugged into pin jacks 45 of the indicator it can be ascertained whether or not the oscillator vtone is being received, and with `the key of switch 40 turned to pad in position meter 36 should deect, reading the loss inthe line (or apparatus). directly in decibels, unless the loss is greater than the 15 d.b. capacity of the scale reading. If the loss is greater than 15 d. b., by turning the key of switch 40 to pad out position the range ofthe indicator is increased to 25 d.b. and the loss of the line (or apparatus) will be the reading of the meter 36 plus 10 d.b., the loss pad 35.

In portable testing sets for measuring transmission e'iciency'of telephone lines as constructed for field service the oscillator unit is equipped for measuring transmission lines and the like having normal characteristics and the best results for example will be obtained when measuring lines or apparatuses'whose impedance at 1000 cycles is approximately 500 to 600 ohmsthe value more generally found in open-wire circuits and equipment. However, correct results' will be obtained with lines and apparatus of other impedances, if the input impedance of the receiving unit is built out to the same impedance as the line or apparatus. That is, if the'circuit impedance is greater than 800 ohms, and has an impedance of R ohms, a resistance whose value is 600 ohms should be connected in series with one of the input terminals of the receiving unit and the line. In Figure 3 a pad 48 is shown connected in the circuit for this purpose. This pad may be a 10 decibel or other value of artificial line unit, as an accessory, foruse as 'a multiplier to increase the lost rangefof the combination. This pad 48 also functions in the combination to provide a loss operating to negative any gain which may occur in a transmission line or apparatus due to amplification or the like whereby the indicator unit meter 36 will be capable of reading such gains in efciency directly in transmission units, the reading indicating a net loss being the difference between the gain in the line and the loss in pad 48 which would necessarily have to be a greater transmission equivalent.

It is frequently desirable, if not essential as in some localities where it is diicult to obtain the plate voltage batteries to provide a transmitting oscillator where such batteries are not required. Such an oscillator is diagrammatically shown in Figure 2 and consists of an extremely light, compact and rugged set for field service having a mechanical type oscillator 49 consisting of an induction coil with a reed type buzzer 50 tuned to vibrate at 1000 cycles per Second,- or a microphone button type of buzzer or the like. This oscillator is supplied by two 4.5 volt dry cell batteries 51 connected in multiple which are placed in a compartment of the case 52 in which all of the oscillator unit apparatus is housed. The secondary coil 53 of the oscillator induction coil 49 feeds into a pad 56 having predetermined transmission equivalents of the character previously described. A meter 57 of the same general character as meter 33 described in connection with the tube type oscillator unit is connected in the output circuit. This meter is provided with a meter shunt 58 connected across its terminals. The unit has terminal members 60 and 6l similar to the members 11 and 12.

In operation the buzzer of induction coil 49 is set into motion upon closing key switch 62 so as to connect battery 51 with the induction coil and the frequency of the buzzer may be checked with a pitch pipe having a frequency of 1000 cycles as previously set forth. The terminals 60 and-'61 vare connected with terminals 16 and 17 of the indicator unit and the output ofthe oscillator is adjusted 'until the indicator meter reads 0 d.b. as previously set forth. The reading of meter 57 is noted and the sets are then ready for testing the transmission line or apparatus to be measured. The units are conwith'the line as indicated in Figure 1 and the current is adjusted so that-meter 57 will read exactly the same amount' as when the indicator stantially the same as previously set forth in the testing of transmission lines in making attenuation measurements where the losses may be of considerable magnitude or on the other hand there may be an actual gain in eiciency. In the same manner measurements of other apparatuses; switch board circuits, such as cord circuits for transmission losses, Vthe exact eni- "ciency of transmitters Vand receivers as well as other functions may be measured with the oscillator and indicatorsets in accordance with this invention.

In the testing `of transmitters and receivers, one method is to connect a standard receiver 64 direct to the oscillator unit terminals, the receiver is placed tightly against the transmitter 65 to be tested as shown in Figure 5, and if the transmitter for example is connected through a standard magneto telephone circuit 66 or the like, to the indicator unit,"the oscillator output will cause a deflection of the indicator from Which the eiciency of the transmitter may be determined. Similarly by using a standard transmitter in the circuit and connecting a receiver to be tested in place of the standard receiver the eficiency of the receiver under test may be determined.

In the testing of the capacity of condensers with these oscillators and indicator units, the condensers may be connected either in series as shown in Figure 6, or in parallel as shown in Figure 7, for either series or parallel losses.

Condensers, resistances, inductances, and other apparatus to be tested are connected at 67, Figure 6, in series with the oscillator and indicator units. The apparatus shown 67, in this instance comprises simplex or phantom repeating coils for unbalanced windings: It is to 'be noted that in testing such coils, both halves of the primary should show the same readings as should also both halves of the secondary. The two primaries, however, may diier slightly from the secondaries without causing trouble.

Such apparatus, drops, relays, etc. are also tested as parallel being connected at 68, Figure 7, with the oscillator and indicator units to determine the amount of their loss when bridged across a talking circuit. As shown, an inductance coil, such as a relay winding, is shown connected at 68.

Referring to Figure 8, the oscillator and indicator units are shown connected with two transmission line circuits 69 and 70 respectively, in order to measure abnormal cross-talk between these two circuits, by noting the amount of oscillator current Vinduced from line to line '10. In this test the ends of the lines are connected with telephones or Geo @nm shprts 7 1 .arid"'72 respectively. The efficiency of both of such 'a pair of transmission lines may be measured in a similar manner by substituting `for' fthe telephones or resistance shorts, conductors 'land '74, tying the distant ends of the lines together as shown in Figure 9, thereby'forming a' loop and measuring the attenuation losses as pre'- viously set forth (providing their combined losses 4do not exceed 30 decibels, the maximum range of the indicator unit). If bothv lines have` the same characteristics, the loss on each line is of course one-half that o i the total loop. this way parallel transmission lines of similar characteristics may b e measured for `transmitting eiiiciency both in line losses and cross-talk.

What is claimed as the invention and is de sired to be secured by Letters Patent i'sz 1. The method of measuring transmission efiieny Q,f telephone linge and th like which consists in impressing an alternating V currentf a predetermined value through" a pad multiplier corresponding to a number ofI transmission units in excess of the maximum transmission units gained by the line section under test toa point ci the line from which measurements'are to be made and simultaneously measuring the proportionate amount of said current received at another peint of the line at the end o f theV section of line under test to indicate the diierence between said pad multiplier and the transmission equivalents of the line, circuit vunder test.

2. In transmission testing the method vfor measuring the efficiency of telephone transmission lines and the like including an oscillator unit having an artificial net work or pad in its output circuit for impressing on a transmission line or the like at one peint an alternating current, and also including an indicator unit having a meter with a scale calibrated in decibels, and the oscillator unit having an output adjustable to a predetermined value o current so that wlrien the indicator unit is connected directly with the oscillator unit transmitting the predetermined value of alternating current it will read Zero decibels and when it is connected at a 'remote point oi the transmission line or the like Will receive a proportionate amount of said transmitter alternating current transmitted corresponding to the efficiency of the circuit between said points and give a scale reading directly in decibels, and including a second separate pad unit having a certain loss in transmission units adapted to be connected in the line under test between the oscillator and indicator unit to counteract any gain in transmission einciency there may be in a line under 4test so that the line eiiciency may be determined by the difference between the loss in the pad and the reading of the meter.

3. In transmission testing apparatus for Ineasuring the efficiency of telephone transmission lines and the like, an oscillator unit including an audion tube oscillator circuit for generating an alternating current and means for varying the frequency thereof, a transformer having its primary connected with the output or said oscillator circuit and an output circuit for impressing oscillations upon the lines or apparatus under test connected with the Secondary Qf S2491 trimsforrner including a rectifying type o f alternating .current measuring .meier and e pgtnligletef @Deer-Pied across the transfqrmer seondary, and e P21@ eRfQi ting ti'gl'idanc of a normal V Qllllpl'l? Qu-it withthevariabie 'terminals 'f 'said "M smission testing apparatus for measuring the ecie'ney d f telephone transmission lines and the"likefanbsscillator 'unit including an audienA tulrie'v 'oscillator 'circuit for lgenerating 'a'ri alternating current' with means for regulating the trequency thereof a transformer having its primary 'eqr'ineted'w'fith'tlie' output of said oscillator cireuit 'an' output circuit for impressing dsillatidns u p'cqntiiey lines or apparatus under"`test connected with the' secondary f vudiifiea re'c'tfying type gfcurrent' measuring meter and a te 'tor regulating the amount of .magnified Tinto' Philips@ er apparatus undef testQand plugging" ininearis for"connecting a phone reyer or th'like with said output ci; .utHfor 'letrirl'Iiri'sA the frequency in 21dthe lla't'olr to the desired'rreguency. .argunfome ne transmission r um? lgns 'alternating curng of n induction ceilwith a tuned "fle @liet the''ergnflery .0f which f` hier naiiirigjits primari connected with 10 'Ch C i .'t .1 utv f saidgfsellaft'or, 'and an output cir- Acuit fif impressing" pseulau fie iipfpii'uie lines qr'anparatus'udertest' po; cted with the secldffsaid.transfermr.'

' 6L 'In transmission testing apparatus for measuringtleeiliciency of "telephone transmission lirleS and thllfe, in whichan' alternating curinf frdtmnd ,e '1S Supplied into the unesjto' betested; an encased indicating unit ineluding'a pad multiplier having a definite loss in 'transmission unitstliroughfwhich alternating 'Current 'frein' @heling flOLWS, a' key type Switch operable'to connect said'p'ad multiplier in the circuit er to exclude lit therefrom, and a rectifying" type of' alternating'''current meter calibra ed in' 'deeibels'corresperiding to the proportions of the alternating current supplied by the Iineunde'r te "'in'transrnission units.

7. vIntrans'iniSsion testingapparatus for measuring'v "ilciency of telephcne transmission lines and the like', means for supplying an alternating eurrent of predetermined value into the'lines to be tested, an indicating unit includa'patl multiplier having a definite loss in transmission units through which alternating current' from the line'flews', a reetifying type of alternating'"curlelit meter calibrated in decibels corresponding tothe proportions of the alterhating current supplied tothe line so as to give direct readings 'of' the eciency of the lines under test intransinlssion units, and plugging rnea'nster connecting a` telephone receiver o1" ,thelil r e"itzithv Seid indicator circuit so as to audibly determine whether the testing alternating'c'urrent'impulses are being received by the indicator unit.

In transmission testing apparatus for mea"- uri'ng the' eiciency of telephone transmission linesand'the'lile, means for supplying an alter- 145 nating current'of predetermined value into the `lines to be tested, ,an indicating unit including a pad multiplier having a definite loss in transmission units through which alternating curfeat. fram the lig'iiwf 'a ker type Switch 0p- 150 erable to connect said pad multiplier in the circuit or to exclude it therefrom, and a rectifying type of alternating current meter calibrated rent from the line flows, a rectifying type of al-' ternating current meter calibrated in decibels correspondingto the proportions of the alternating current supplied by the line and a manually operated switch associated with said pad operable to connect the pad in the circuit to provide for the direct scale readings of transmission units and operable to exclude the pad whereby the transmission loss of the pad will be added to the reading of the meter to thereby extend the loss range of the indicator unit.

10. In transmission testing apparatus for measuring the efficiency of telephone transmissionl lines and the like, means for supplying an alternating current of predetermined value into the lines to be tested, an indicating unitincluding a pad multiplier having a denite loss in transmission units through which alternating current from the line flows, a rectifying type of alternating current meter calibrated in decibels corresponding to the proportions of the alternating current supplied to the line so as to give direct readings of the' eiciency of the lines under test in transmission units, and a choke coil inductance connected with the leads of said indicator unit for absorbing undesired oscillations or line disturbances at other frequencies than the frequency of thev test alternating current supplied tothe line so that the meter readings will be unaffected thereby.

11. -The method of measuring pairs of transmission lines for cross-talk and loop attenua-- tion losseslwhich consists in impressing on one of the lines an attenuating current of a predetermined value and noting the amount of current induced in the other line and the propor-` ing current of a predetermined value on a receiving indicator connected therewith, bridging the apparatus across the connections with the receiving indicator and then noting the proportionate amount of said current received by lthe receiving indicator.

LEn E. ADLER. 

